Question

A disaccharide X does NOT show mutarotation in aqueous solution. Acidic hydrolysis of X affords two different monosaccharides. The disaccharide X is:

• A.
• B.
• C.
• D.

Hint:

Disaccharides like sucrose that involve both anomeric carbons in glycosidic bonding do not show mutarotation. Hydrolysis giving two different sugars confirms the presence of two different monosaccharide units.

Answer 1

The Correct Option is D

The key to solving this question lies in understanding the structural features responsible for mutarotation.

• Mutarotation occurs due to the interconversion between \( \alpha \)- and \( \beta \)-anomers of a sugar, which requires a free anomeric carbon.
• If the anomeric carbon of both monosaccharide units in a disaccharide is involved in the glycosidic linkage, then the sugar does not show mutarotation.
• Among the options, structure (D) is sucrose, a disaccharide of glucose and fructose joined by a 1,2-glycosidic bond between both anomeric carbons.

In sucrose:

• The \( \alpha \)-anomeric carbon of glucose and the \( \beta \)-anomeric carbon of fructose are involved in the linkage.
• Therefore, no free anomeric carbon is available, and mutarotation is not possible.
• Hydrolysis of sucrose gives two different monosaccharides: glucose and fructose.

\[ \boxed{\text{Disaccharide X is sucrose (Option D), which does not show mutarotation.}} \]